Tunable emission and thermal sensitivity via energy transfer from Bi³⁺ to Eu³⁺ in BaY₂Al₂Ga₂GeO₁₂

BaY₂Al₂Ga₂GeO₁₂ (BYAGGO):Eu³⁺ and BaY₂Al₂Ga₂GeO₁₂:0.03Bi³⁺, yEu³⁺ phosphors have been prepared via a high-temperature solid phase method. BYAGGO:Eu³⁺ has a stronger characteristic emission of Eu³⁺ at 592 nm attributed to magneto-dipole transitions under 245 nm excitation, indicating that Eu³⁺ is more inclined to occupy the central lattice of the octahedron with inverted symmetry. The lattice of Eu³⁺ ions expands to the asymmetric dodecahedron center in Eu³⁺ and Bi³⁺ ions co-doped in BYAGGO. The emission of BYAGGO:Bi³⁺ overlaps the excitation of BYAGGO:Eu³⁺, implying that energy transfer (ET) from Bi³⁺ to Eu³⁺ is possible. Furthermore, the fluorescence decay lifetime is the direct proof of energy transfer in BaY₂Al₂Ga₂GeO₁₂:0.03Bi³⁺, yEu³⁺. The energy transfer efficiency reaches 72% at y = 0.25. Finally, BYAGGO:0.03Bi³⁺, 0.09Eu³⁺ phosphor is employed for a WLED device with a color temperature of 3825 K and a color rendering index (Ra) of 88.75.